The American Society for Microbiology (ASM) is submitting comments on the proposed policy for National Pollutant Discharge Elimination System (NPDES) Permit Requirements for Wastewater Discharges During Wet Weather (Docket ID No. OW-2003-0025). The following comments were developed by ASM’s Committee on Environmental Microbiology’s Subcommittee on Water, of the Public and Scientific Affairs Board.

The ASM is the premier educational and scientific society dedicated to the advancement of microbiological research and its application for the common good. The Society represents more than 42,000 microbiologists, including scientists in academic, industrial and government institutions, working in a variety of areas, including medical, genomic, molecular, environmental and food microbiology, and public health.

We commend the Environmental Protection Agency (EPA) for addressing the ecological and human health effects on our nation’s water systems from the impacts of wet weather on wastewater discharges. Additionally, we are pleased to see that the proposed policy acknowledges the importance of maintaining secondary treatment standards in blended effluents when blending is necessitated by excess water inputs to wastewater treatment systems.

We also recognize the substantial challenges to extant wastewater treatment facilities posed by high rates of infiltration and inflow that occur during periods of wet weather, and that maintaining acceptable water quality standards during periods of wet weather requires:

1) careful consideration of the short-term and long-term impacts of blending;2) analysis of treatment protocols to ensure that they are adequate for reducing pathogenic microbes to target levels or lower;3) developing appropriate monitoring and reporting protocols.

We further recognize that problems posed by wet weather may become even more important in the future due to the impacts of climate change. Regions that currently experience limited blending may find that the frequency of blended discharges increases.

Unfortunately, we are concerned that the proposed policy may provide inadequate control of microorganisms that pose significant threats to human health through contamination of sources used for potable water supplies in particular. While the proposed policy intends to maintain water quality standards based on biochemical oxygen demand (BOD) and suspended solids, and provides for water quality monitoring, there is no explicit requirement to control pathogenic microorganisms in blended discharges to acceptable levels.

We offer the following recommendations in an effort to address public health deficiencies and environmental quality issues found in the proposed policy.

1. ISSUE: The potential impacts of the proposed blending policy have not been assessed using a microbial risk analysis approach that could help identify hazards and provide input for determining overall costs and benefits of the policy.

SOLUTION: Potential hazards from pathogenic microorganisms should be assessed using a microbial risk analysis based on realistic loading rates and data. Such an assessment should specify target levels of pathogens (viruses, bacteria and protozoa) and indicator organisms and identify levels of removal needed to achieve the targets.

2. ISSUE: The proposed policy does not address the potential for pathogen (bacteria) regrowth in blended effluents subsequent to discharge.

SOLUTION: Regrowth potential needs to be assessed empirically using a range of blended discharges representative of typical waste streams produced during periods of peak infiltration and inflow. Specifically, levels of disinfection that prevent pathogen regrowth must be assessed empirically.

3. ISSUE: Levels of disinfection that prevent pathogen regrowth may vary from system to system and as a function of storm water loading. The proposed blending policy does not explicitly address variability in disinfection efficacy.

SOLUTION: Levels of disinfection that prevent pathogen regrowth must be assessed empirically using a range of conditions representative of blended effluents that would be discharged in practice.

4. ISSUE: Discharge of blended effluents may result in increased sediment loading and deposition within receiving waters using 30-day averages of BOD and suspended solids as criteria for permits. The impacts of increased sediment loads on water quality are not known and are not addressed by the proposed policy.

SOLUTION: The impacts of a realistic range of sediment loading and deposition on water quality should be addressed empirically and through suitable water quality modeling efforts to ensure that long-term degradation of water quality does not occur due to blended discharges.

5. ISSUE: The proposed policy recognizes current needs due to periods of wet weather, but does not provide a provision for addressing the current or future scope of the problem.

SOLUTION: EPA should work with climate modelers, hydrologists and wastewater treatment facilities to assess current temporal and regional trends in the frequency and volume of blended discharges, and to develop predictive models of future trends. Predictive models should be used to inform the design of future treatment facilities with a goal of minimizing blended discharges.

Serious human health risks based on exposure to a variety of microbial pathogens may result from blended discharges unless the proposed policy is modified to monitor and control the pathogens of concern. Therefore, we encourage the EPA to include microbial-based monitoring and standard setting, along with science-based risk reductions to ensure a healthy environment and provide adequate public health safety.

We are pleased to have the opportunity to provide comments in response to the proposed policy on the NPDES permit regulation for wastewater discharges during periods of wet weather, and hope that these comments and recommendations are of assistance to the EPA.